[PATCH] Add new ubegin/uend API to StringRef/MDString

[Duncan P. N. Exon Smith]

> On 2014-Nov-13, at 10:35, David Blaikie <dblaikie at gmail.com> wrote:
> 
> 
> 
> On Thu, Nov 13, 2014 at 4:39 AM, Duncan P. N. Exon Smith <dexonsmith at apple.com> wrote:
> 
> > On 2014 Nov 12, at 16:55, Keno Fischer <kfischer at college.harvard.edu> wrote:
> >
> > Hi dexonsmith,
> >
> > In some instances (such as in BitCodeWriter - see http://reviews.llvm.org/D6184),
> > it is useful to get an unsiged version of the data pointer instead. This adds an
> > appropriate API to be used in BitCodeWriter in a follow up commit.
> >
> > http://reviews.llvm.org/D6241
> >
> > Files:
> >  include/llvm/ADT/StringRef.h
> >  include/llvm/IR/Metadata.h
> > <D6241.16125.patch>
> 
> This LGTM.  I have minor nitpicks below that you can take or leave.
> 
> @David, does this API make sense to you given Keno's use case [1]?
> 
> While it matches that use case quite well (needing iterator begin/end) there are many other cases where we play the same game - getting uint8_t rather than just unsigned char:
> 
> lib/Support/DataExtractor.cpp:  return getU<uint8_t>(offset_ptr, this, IsLittleEndian, Data.data());
> lib/Support/MD5.cpp:  const uint8_t *Ptr = Data.data();
> lib/Support/MD5.cpp:  ArrayRef<uint8_t> SVal((const uint8_t *)Str.data(), Str.size());
> lib/IR/Constants.cpp:    const uint8_t *Data = reinterpret_cast<const uint8_t *>(Str.data());
> lib/ProfileData/CoverageMappingReader.cpp:  Result = decodeULEB128(reinterpret_cast<const uint8_t *>(Data.data()), &N);
> lib/ProfileData/CoverageMappingReader.cpp:      decodeULEB128(reinterpret_cast<const uint8_t *>(Data.data()), &N);
> lib/ProfileData/CoverageMappingReader.cpp:      decodeULEB128(reinterpret_cast<const uint8_t *>(Data.data()), &N);
> lib/ExecutionEngine/RuntimeDyld/RuntimeDyldChecker.cpp:        reinterpret_cast<const uint8_t *>(SectionMem.data()),
> lib/ExecutionEngine/Interpreter/ExternalFunctions.cpp:  uint8_t *ArgDataPtr = ArgData.data();
> lib/DebugInfo/DWARFFormValue.cpp:      Value.data = reinterpret_cast<const uint8_t *>(str.data());
> include/llvm/Support/FileOutputBuffer.h:    return (uint8_t*)Region->data();
> include/llvm/Support/FileOutputBuffer.h:    return (uint8_t*)Region->data() + Region->size();
> include/llvm/Object/ELF.h:    return reinterpret_cast<const uint8_t *>(Buf.data());
> include/llvm/MC/YAML.h:      : Data(reinterpret_cast<const uint8_t *>(Data.data()), Data.size()),
> tools/llvm-objdump/llvm-objdump.cpp:    ArrayRef<uint8_t> Bytes(reinterpret_cast<const uint8_t *>(BytesStr.data()),
> tools/llvm-objdump/MachODump.cpp:    ArrayRef<uint8_t> Bytes(reinterpret_cast<const uint8_t *>(BytesStr.data()),
> tools/llvm-mc/Disassembler.cpp:  ArrayRef<uint8_t> Data(Bytes.first.data(), Bytes.first.size());
> tools/llvm-readobj/StreamWriter.h:    auto V = makeArrayRef(reinterpret_cast<const uint8_t*>(Value.data()),
> tools/llvm-readobj/StreamWriter.h:    auto V = makeArrayRef(reinterpret_cast<const uint8_t*>(Value.data()),
> tools/llvm-readobj/StreamWriter.h:    auto V = makeArrayRef(reinterpret_cast<const uint8_t*>(Value.data()),
> tools/llvm-readobj/StreamWriter.h:    auto V = makeArrayRef(reinterpret_cast<const uint8_t*>(Value.data()),
> 
> In several of these cases we're interested in getting an ArrayRef<uint8_t> from the StringRef - so maybe that's a better primitive operation (it's annoying when interoperating with containers, I'll grant you - since you need to call it twice, or stash a local variable - but one day... we'll have range algorithms for this sort of thing - in the mean time we could have utility functions like those in this patch, but I think the primary operation should probably be "give me a raw (uint8_t) byte array for this StringRef")
> 

Sure.  Do you have a name in mind?  `uref()`?

> Also see Aaron's recent -Wcast-qual fixing patches that touched several cases like this: 
> http://llvm.org/viewvc/llvm-project?view=revision&revision=221782
> http://llvm.org/viewvc/llvm-project?view=revision&revision=221781
>  
> 
> [1]: http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20141103/243658.html
> 
> > Index: include/llvm/ADT/StringRef.h
> > ===================================================================
> > --- include/llvm/ADT/StringRef.h
> > +++ include/llvm/ADT/StringRef.h
> > @@ -40,6 +40,7 @@
> >    class StringRef {
> >    public:
> >      typedef const char *iterator;
> > +    typedef unsigned const char *uiterator;
> 
> This spelling is strange to me; I'd expect:
> 
>     typedef const unsigned char *uiterator;
> 
> >      typedef const char *const_iterator;
> >      static const size_t npos = ~size_t(0);
> >      typedef size_t size_type;
> > @@ -88,8 +89,12 @@
> >      /// @{
> >
> >      iterator begin() const { return Data; }
> > +    uiterator ubegin() const { return reinterpret_cast<uiterator>(Data); }
> 
> I have a slight preference for:
> 
>     uiterator ubegin() const { return reinterpret_cast<uiterator>(begin()); }
> 
> But mainly just to match my change to `uend()` below.
> 
> >
> >      iterator end() const { return Data + Length; }
> > +    uiterator uend() const {
> > +      return reinterpret_cast<uiterator>(Data) + Length;
> > +    }
> 
> I think this should be:
> 
>     uiterator uend() const { return reinterpret_cast<uiterator>(end()); }
> 
> >
> >      /// @}
> >      /// @name String Operations
> > Index: include/llvm/IR/Metadata.h
> > ===================================================================
> > --- include/llvm/IR/Metadata.h
> > +++ include/llvm/IR/Metadata.h
> > @@ -55,12 +55,15 @@
> >    unsigned getLength() const { return (unsigned)getName().size(); }
> >
> >    typedef StringRef::iterator iterator;
> > +  typedef StringRef::uiterator uiterator;
> >
> >    /// \brief Pointer to the first byte of the string.
> >    iterator begin() const { return getName().begin(); }
> > +  uiterator ubegin() const { return getName().ubegin(); }
> >
> >    /// \brief Pointer to one byte past the end of the string.
> >    iterator end() const { return getName().end(); }
> > +  uiterator uend() const { return getName().uend(); }
> >
> >    /// \brief Methods for support type inquiry through isa, cast, and dyn_cast.
> >    static bool classof(const Value *V) {
> >
> 
>